.223 versus 5.56mm
 

There are a number of surplus arm around in .223 Remington caliber and others that are 5.56mm. There is a difference between these two cartridges. The link below covers the topic very well. You can fire .223 ammo safely in a 5.56mm chamber. Going the reverse route can be a problem. All the best...
Gil


http://www.thegunzone.com/556v223.html

Gil,

Good post. My smallest centerfire on establishment is the .243, so 5.56mm or .223 is not much concern to me. However, on page 22 of "Cartridges of the World, 9th Edition", Frank C. Barnes states, "military ball ammo may produce high chamber pressure in (.223) sporting rifles.

Adam